Connecting classification with systematics

Connecting classification with phylogeny

Using phylogeny to trace the relatives of birds

Each tree is a hypothesis about the most likely path of evolution based on the data available



  • What makes a bird a bird?


  • Shared ancestral character: a trait that is found in the ancestor of a group and all of the derived taxa have the trait
    • common ancestor for all taxa at root of the tree


  • Critical innovations = Shared Derived Character
    • adaptive traits that define new taxa
    • marked with ‘slashes’ on tree
    • evolutionary novelties to distinguish taxa

Anatomy of a phylogenetic tree

How to draw phylogenies: branch shape and length

Length of branch represents evolutionary time from a common ancestor (units can vary)

How to draw phylogenies: branch shape and length

Mapping traits on a phylogeny (review homology)

Convergent evolution in marine mammals (analogous traits)

Aquatic mammals are a large polyphyletic group in the mammal phylogeney

How to use derived characters to infer phylogeny

How to use derived characters to infer phylogeny





  • Principle of Parsimony = Simplest solution is the likely path of evolution


  • A logical way to identify homologous and analogous traits


  • Minimize the # of evolutionary changes needed to explain your character data

How to use derived characters to infer phylogeny

Visualizing Parsimony (homology vs analogy)

Whale Evolution: A Case History



  • Phylogenetic trees based on morphology place whales outside of the artiodactyl group


  • Artiodactyl mammals = cows, deer and hippos
    • hooves with even number of toes
    • unusual pulley-shaped ankle bone


  • Astragalus ankle bone is a shared derived trait for all artiodactyls
    • the principle of parsimony, based on this trait, should exclude whales

Whale Evolution: A Case History



  • How do we determine evol’n relationships?
    • morphology - presence/absence of ankle bone
    • DNA sequences - shared gene families


  • Depends on what data you have!
    • poor fossil records make this tricky


  • Modern genetic data now suggests a closer relationship between whales and hippos…

Whale Evolution: Whales and Hippos share common ancestor